31.3.3.7 Temperature Measurement

An on-chip temperature sensor is available. To do a temperature measurement, follow these steps:

1. Configure the voltage reference to internal 1.024V by writing to the Reference Selection (REFSEL) bit field the ADCn.CTRLC register.
2. Select the temperature sensor as input in the Positive Input Multiplexer (ADCn.MUXPOS) register.
3. Configure the ADC Sample Duration by writing a value ≥ $32\mathrm{\mu s}\times f_{\text{CLK\_ADC}}$ to the Sample Duration (SAMPDUR) bit field in the Control E (ADCn.CTRLE) register.
4. Acquire the temperature sensor output voltage by running a 12-bit Single-Ended conversion.
5. Process the measurement result, as described below.

The measured voltage has a linear relationship to the temperature. Due to process variations, the temperature sensor output voltage varies between individual devices at the same temperature. The individual compensation factors determined during the production test are stored in the Signature Row:

• SIGROW.TEMPSENSE0 is a gain/slope correction
• SIGROW.TEMPSENSE1 is an offset correction

To achieve more accurate results, the result of the temperature sensor measurement must be processed in the application software using compensation values from device production or user calibration. Refer to the Electrical Characteristics section for further details.

The following equation is used to calculate the temperature (in Kelvin):

$T=\frac{(\text{ADC Result}+\text{Offset})\times \text{Slope}}{4096}$

It is recommended to follow these steps in the user code when using the compensation values from the Signature Row:

#define SCALING_FACTOR 4096 // Enables integer in the signature row

int16_t sigrow_offset = (int16_t) SIGROW.TEMPSENSE1; // Read signed offset from signature row
int16_t sigrow_slope = (int16_t) SIGROW.TEMPSENSE0; // Read signed slope from signature row
uint16_t adc_reading = ADC0.RESULT; // ADC conversion result 

int32_t temp = ((int32_t) adc_reading) + sigrow_offset;
temp *= sigrow_slope; // Result can overflow 16-bit variable 
temp += SCALING_FACTOR / 2; // Ensures correct rounding on division below
temp /= SCALING_FACTOR; // Round to the nearest integer in Kelvin
uint16_t temperature_in_K = (uint_16t) temp;
int16_t temperature_in_C = temp - 273;